43 lines
1.4 KiB
JavaScript
43 lines
1.4 KiB
JavaScript
// The event loop's JS side. The host owns the loop (see lib/rt/jsrt.h). A
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// macrotask is an IO op or a timer, which the host runs: it calls
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// `__complete(h)` when op `h` is done. A microtask is a promise job, in
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// `__microtasks`. After the program's top level, end.js runs all microtasks,
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// and after each macrotask, `__complete` does
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// What to do when IO op `h` completes: `__pending[h]`, a fn that gets `h`.
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// Handles are small ints, and a handle is used again after its op completes
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const __pending = [];
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// Promise jobs, in order. `head` is the next one, so that taking a job does
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// not move the others. A job is a closure, which keeps its own data: the
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// handler and the value that it is called with. So each handler gets only the
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// values of its own promise (see `docs/model.md`, section 3.3)
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const __microtasks = { jobs: [], head: 0 };
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function __queue_job(job) {
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__microtasks.jobs.push(job);
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}
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function __drain_microtasks() {
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const q = __microtasks;
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while (q.head < q.jobs.length) {
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const job = q.jobs[q.head];
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q.jobs[q.head] = undefined;
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q.head++;
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job();
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}
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q.jobs.length = 0;
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q.head = 0;
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}
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// What the host calls when op `h` is done: its callback, then the microtasks.
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// The compiler finds it by name
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function __complete(h) {
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const done = __pending[h];
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__pending[h] = undefined;
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if (done !== undefined) done(h);
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__drain_microtasks();
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}
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